A Roland VG-8 modeling guitar synth was used for the Love solo on Mellon Collie. It connects to a special additional split "synthesizer" pickup (GK-2A, now GK-3), and emulates the sounds of various types of guitars, pickups, and amps (a feature now common in multi-effect pedals like the Boss GT series, etc.).
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James and Billy recall the recording:

[James:] "since we wanted something cyber-like, I tried a Roland guitar synthesizer. I sat there for four hours, and finally walked out of the room and said, 'I can't get anything out of this.'" Corgan had the same luck, but decided to go further into cyberspace, renting a Roland VG-8--a device that reproduces real guitar sounds--something that he had a, shall we say, philosophical problem with. "Why the fuck would you want a device that makes your guitar sound like a fucking guitar?!" he crows. "They've got a Twin Reverb sound on there, and a metal setting called something like 'HEVE METTLE' and it's the worst sound-- probably Tommy Tedesco's idea of what a distorted metal guitar sounds like." (-Guitar Player, Jan. 1996)